The proliferation of radio frequency (RF) systems and components have increased greatly in recent years. Cable television systems have introduced RF components into millions of homes, and the number continues to grow every year. RF components have also become much more complex as cable television companies offer an increasing array of services, and consumers continue to demand more features from cable television suppliers such as movies on demand, phone services and other interactive services.
The complexity of the RF devices, such as cable television channel selector units, video cassette recorders and cable-ready televisions, greatly increases the number of electronic components contained within each device. The electronics within RF devices include amplifiers, microprocessors and other semiconductor components. These components are easily damaged when exposed to electrical voltage or current surges from outside sources. RF transmission lines are subject to electrical transients and faults, which may be introduced to the RF devices, causing damage to sensitive electronic components.
Accordingly, protection is needed for the sensitive electronic components within an RF device from damage caused by electrical transients on RF transmission lines and sources.
There are several well known techniques for preventing undesirable electrical surges in RF transmission lines from causing damage to electronic components. One technique is to filter the input by inserting an inductor between the input transmission line and the RF device. The filter suppresses the transient by diverting energy from the RF device, and preventing most of the energy from the transient from reaching the RF device. The magnitude of the transient, although reduced, is still significant enough to cause considerable damage to sensitive electronic components within RF devices.
The use of an inductor as a filter is conventionally enhanced by coupling the inductor with a gas discharge tube. This has been the industry standard for over 30 years. The gas discharge tube greatly increases the ability of the inductor to suppress large electrical transients. However, gas discharge tubes are relatively expensive for this type of application and their service life is limited to only a small number of electrical transients.
Another common surge suppression technique utilized for electronic applications is to buffer the device from the input line with a transformer. Although this provides adequate surge protection, the performance of conventional transformers degrade as the frequency increases. For wide band RF devices, conventional transformer surge suppression is not acceptable since the ferrite core will not carry the RF signal energy from the primary side to the secondary side.
Applicant has recognized that there is a need to develop a more economical electrical surge protection device for wide band RF applications.